A high-content EMT screen identifies multiple receptor tyrosine kinase inhibitors with activity on TGFß receptor.

An epithelial to mesenchymal transition (EMT) enables epithelial tumor cells to break out of the primary tumor mass and to metastasize. Understanding the molecular mechanisms driving EMT in more detail will provide important tools to interfere with the metastatic process. To identify pharmacological modulators and druggable targets of EMT, we have established a novel multi-parameter, high-content, microscopy-based assay and screened chemical compounds with activities against known targets. Out of 3423 compounds, we have identified 19 drugs that block transforming growth factor beta (TGFß)-induced EMT in normal murine mammary gland epithelial cells (NMuMG). The active compounds include inhibitors against TGFß receptors (TGFBR), Rho-associated protein kinases (ROCK), myosin II, SRC kinase and uridine analogues. Among the EMT-repressing compounds, we identified a group of inhibitors targeting multiple receptor tyrosine kinases, and biochemical profiling of these multi-kinase inhibitors reveals TGFBR as a thus far unknown target of their inhibitory spectrum. These findings demonstrate the feasibility of a multi-parameter, high-content microscopy screen to identify modulators and druggable targets of EMT. Moreover, the newly discovered "off-target" effects of several receptor tyrosine kinase inhibitors have important consequences for in vitro and in vivo studies and might beneficially contribute to the therapeutic effects observed in vivo.

Treatment of experimental human breast cancer and lung cancer brain metastases in mice by macitentan, a dual antagonist of endothelin receptors, combined with paclitaxel.

BACKGROUND: We recently demonstrated that brain endothelial cells and astrocytes protect cancer cells from chemotherapy through an endothelin-dependent signaling mechanism. Here, we evaluated the efficacy of macitentan, a dual endothelin receptor (ETAR and ETBR) antagonist, in the treatment of experimental breast and lung cancer brain metastases. METHODS: The effect of macitentan on astrocyte- and brain endothelial cell-mediated chemoprotective properties was measured in cytotoxic assays. We compared survival of mice bearing established MDA-MB-231 breast cancer or PC-14 non-small cell lung cancer (NSCLC) brain metastases that were treated with vehicle, macitentan, paclitaxel, or macitentan plus paclitaxel. Cell division, apoptosis, tumor vasculature, and expression of survival-related proteins were assessed by immunofluorescent microscopy. RESULTS: Cancer cells and tumor-associated endothelial cells expressed activated forms of AKT and MAPK in vehicle- and paclitaxel-treated groups in both metastasis models, but these proteins were downregulated in metastases of mice that received macitentan. The survival-related proteins Bcl2L1, Gsta5, and Twist1 that localized to cancer cells and tumor-associated endothelial cells in vehicle- and paclitaxel-treated tumors were suppressed by macitentan. Macitentan or paclitaxel alone had no effect on survival. However, when macitentan was combined with paclitaxel, we noted a significant reduction in cancer cell division and marked apoptosis of both cancer cells and tumor-associated endothelial cells. Moreover, macitentan plus paclitaxel therapy significantly increased overall survival by producing complete responses in 35 of 35 mice harboring brain metastases. CONCLUSIONS: Dual antagonism of ETAR and ETBR signaling sensitizes experimental brain metastases to paclitaxel and may represent a new therapeutic option for patients with brain metastases.

Macitentan, a Dual Endothelin Receptor Antagonist, in Combination with Temozolomide Leads to Glioblastoma Regression and Long-term Survival in Mice.

PURPOSE: The objective of the study was to determine whether astrocytes and brain endothelial cells protect glioma cells from temozolomide through an endothelin-dependent signaling mechanism and to examine the therapeutic efficacy of the dual endothelin receptor antagonist, macitentan, in orthotopic models of human glioblastoma. EXPERIMENTAL DESIGN: We evaluated several endothelin receptor antagonists for their ability to inhibit astrocyte- and brain endothelial cell-induced protection of glioma cells from temozolomide in chemoprotection assays. We compared survival in nude mice bearing orthotopically implanted LN-229 glioblastomas or temozolomide-resistant (LN-229(Res) and D54(Res)) glioblastomas that were treated with macitentan, temozolomide, or both. Tumor burden was monitored weekly with bioluminescence imaging. The effect of therapy on cell division, apoptosis, tumor-associated vasculature, and pathways associated with cell survival was assessed by immunofluorescent microscopy. RESULTS: Only dual endothelin receptor antagonism abolished astrocyte- and brain endothelial cell-mediated protection of glioma cells from temozolomide. In five independent survival studies, including temozolomide-resistant glioblastomas, 46 of 48 (96%) mice treated with macitentan plus temozolomide had no evidence of disease (P < 0.0001), whereas all mice in other groups died. In another analysis, macitentan plus temozolomide therapy was stopped in 16 mice after other groups had died. Only 3 of 16 mice eventually developed recurrent disease, 2 of which responded to additional cycles of macitentan plus temozolomide. Macitentan downregulated proteins associated with cell division and survival in glioma cells and associated endothelial cells, which enhanced their sensitivity to temozolomide. CONCLUSIONS: Macitentan plus temozolomide are well tolerated, produce durable responses, and warrant clinical evaluation in glioblastoma patients.

Discovery and optimization of 4,5-diarylisoxazoles as potent dual inhibitors of pyruvate dehydrogenase kinase and heat shock protein 90.

Upregulation of pyruvate dehydrogenase kinase (PDHK) has been observed in a variety of cancers. Inhibition of PDHK offers an attractive opportunity for the development of novel cancer therapies. To obtain novel PDHK inhibitors, we took advantage of the homology of the ATP-binding pocket between Heat Shock Protein 90 (HSP90) and PDHK, and utilized 4,5-diarylisoxazole based HSP90 inhibitor for structural design. Our efforts led to the identification of 5k that inhibited PDHK1 with an IC50 value of 17 nM, which, however, showed marginal cellular activity. Further structural optimization resulted in compound 11a with improved cellular activity which could effectively modulate the metabolic profile of cancer cells and lead to the inhibition of cancer cell proliferation, evidenced by the increased oxidative phosphorylation and decreased glycolysis and associated oxidative stress. Our results suggested 11a as an excellent lead compound and a favorable biological tool to further evaluate the therapeutic potential of PDHK and HSP90 dual inhibitors in the treatment of cancer.

An isogenic cell panel identifies compounds that inhibit proliferation of mTOR-pathway addicted cells by different mechanisms.

The mTOR pathway is a critical integrator of nutrient and growth factor signaling. Once activated, mTOR promotes cell growth and proliferation. Several components of the mTOR pathway are frequently deregulated in tumors, leading to constitutive activation of the pathway and thus contribute to uncontrolled cell growth. We performed a high-throughput screen with an isogenic cell line system to identify compounds specifically inhibiting proliferation of PTEN/mTOR-pathway addicted cells. We show here the characterization and mode of action of two such compound classes. One compound class inhibits components of the PTEN/mTOR signaling pathway, such as S6 ribosomal protein phosphorylation, and leads to cyclin D3 downregulation. These compounds are not adenosine triphosphate competitive inhibitors for kinases in the pathway, nor do they require FKBP12 for activity like rapamycin. The other compound class turned out to be a farnesylation inhibitor, blocking the activity of GTPases, as well as an inducer of oxidative stress. Our results demonstrate that an isogenic cell system with few specific mutations in oncogenes and tumor suppressor genes can identify different classes of compounds selectively inhibiting proliferation of PTEN/mTOR pathway-addicted isogenic clones. The identified mechanisms are in line with the known cellular signaling networks activated by the altered oncogenes and suppressor genes in the isogenic system.

Metastatic disease: a drug discovery perspective.

Disseminated tumor cells are present in many patients at diagnosis. At a time when the disseminated disease becomes prominent, patients have already been treated with many cycles of therapy to which their metastases were also exposed. These metastases have genetically evolved from primary tumors. Furthermore, their interaction with the tissue microenvironment plays an important role in all phases of disease development. These facts have only partially been taken into consideration when profiling anti-cancer compounds foreseen to treat patients with disseminated metastatic disease. In this perspective, we discuss the unique features of metastatic disease and review the model systems available for drug profiling. Based on an analysis of how compounds are profiled today in pre-clinical models of metastatic disease and what would be desirable and possible with the present know-how, we recommend a refined profiling process to validate drugs with potential to treat patients with overt metastatic disease.

Antivascular therapy for multidrug-resistant ovarian tumors by macitentan, a dual endothelin receptor antagonist.

Endothelin receptors (ETRs) are often overexpressed in ovarian tumors, which can be resistant to conventional therapies. Thus, we investigated whether blockage of the ETR pathways using the dual ETR antagonist macitentan combined with taxol or cisplatinum can produce therapy for orthotopically growing multidrug-resistant (MDR) human ovarian carcinoma. In several studies, nude mice were injected in the peritoneal cavity with HeyA8-MDR human ovarian cancer cells. Ten days later, mice were randomized to receive vehicle (saline), macitentan (oral, daily), taxol (intraperitoneal, weekly), cisplatinum (intraperitoneal, weekly), macitentan plus taxol, or macitentan plus cisplatinum. Moribund mice were killed, and tumors were collected, weighed, and prepared for immunohistochemical analysis. The HeyA8-MDR tumors did not respond to taxol, cisplatinum, or macitentan administered as single agents. In contrast, combination therapy with macitentan and taxol or macitentan and cisplatinum significantly decreased the tumor incidence and weight and significantly increased the survival of mice and their general condition. Multiple immunohistochemical analyses revealed that treatment with macitentan and macitentan plus taxol or cisplatinum inhibited the phosphorylation of ETRs, decreased the levels of pVEGFR2, pAkt, and pMAPK in tumor cells after 2 weeks of treatment and induced a first wave of apoptosis in tumor-associated endothelial cells followed by apoptosis in surrounding tumor cells. Our study shows that ovarian cancer cells, which express the endothelin axis and are multidrug resistant, are exquisitely sensitive to treatment with a dual ET antagonist and can be resensitized to both taxol and cisplatinum. This combined therapy led to a significant reduction in tumor weight.

Antitumor compound testing in glioblastoma organotypic brain cultures.

Glioblastoma multiforme (GBM) is the most common and most aggressive type of primary brain tumor. Identification of new therapeutic regimens is urgently needed. A major challenge remains the development of a relevant in vitro model system with the necessary capacity and flexibility to profile compounds. The authors have developed and characterized a 3D culture system of brain cells (brain Hi-Spot) where GBM-derived cells can be incorporated (GBM/brain Hi-Spot). Immuno-fluorescence and electrophysiological recordings demonstrate that brain Hi-Spots recapitulate many features of brain tissue. Within this tissue, GBM-derived cell growth is monitored using a fluorescence assay. GBM-derived cells growing in Hi-Spots form tumor nodules that display properties of GBM such as 5-Ala positive staining, an acidic environment, and tumor-surrounding astrocyte activation. Temozolomide inhibits GBM growth in brain Hi-Spots, but it is not effective in 2D cultures. Other chemotherapeutics that have proven to be inefficient in GBM treatment display low activity against GBM-derived cells growing in brain Hi-Spots in comparison to their activity against GBM 2D cultures. These findings suggest that GBM/brain Hi-Spots represent a simple system to culture cells derived from brain tumors in an orthotopic environment in vitro and that the system is reliable to test GBM targeting compounds.

Macitentan (ACT-064992), a tissue-targeting endothelin receptor antagonist, enhances therapeutic efficacy of paclitaxel by modulating survival pathways in orthotopic models of metastatic human ovarian cancer.

Potential treatments for ovarian cancers that have become resistant to standard chemotherapies include modulators of tumor cell survival, such as endothelin receptor (ETR) antagonist. We investigated the therapeutic efficacy of the dual ETR antagonist, macitentan, on human ovarian cancer cells, SKOV3ip1 and IGROV1, growing orthotopically in nude mice. Mice with established disease were treated with vehicle (control), paclitaxel (weekly, intraperitoneal injections), macitentan (daily oral administrations), or a combination of paclitaxel and macitentan. Treatment with paclitaxel decreased tumor weight and volume of ascites. Combination therapy with macitentan and paclitaxel reduced tumor incidence and further reduced tumor weight and volume of ascites when compared with paclitaxel alone. Macitentan alone occasionally reduced tumor weight but alone had no effect on tumor incidence or ascites. Immunohistochemical analyses revealed that treatment with macitentan and macitentan plus paclitaxel inhibited the phosphorylation of ETRs and suppressed the survival pathways of tumor cells by decreasing the levels of pVEGFR2, pAkt, and pMAPK. The dose of macitentan necessary for inhibition of phosphorylation correlated with the dose required to increase antitumor efficacy of paclitaxel. Treatment with macitentan enhanced the cytotoxicity mediated by paclitaxel as measured by the degree of apoptosis in tumor cells and tumor-associated endothelial cells. Collectively, these results show that administration of macitentan in combination with paclitaxel prevents the progression of ovarian cancer in the peritoneal cavity of nude mice in part by inhibiting survival pathways of both tumor cells and tumor-associated endothelial cells.